The following invention relates generally to a natural gas detection apparatus and method, and in particular to an optical natural gas detector for mounting on a natural gas leak survey vehicle.
By federal regulation, the natural gas industry must periodically survey the entire natural gas distribution network for leaks. Currently, the network includes approximately 1.59 million miles of underground pipeline. This vast network of underground natural gas pipeline must be surveyed by natural gas personnel either on foot or by vehicle.
Natural gas personnel face significant obstacles when surveying for underground gas leaks. An effective gas detection device must effectively and economically overcome these obstacles.
First, before being detectable, the gas must filter up through the soil. If the gas pipeline is buried beneath a street, sidewalk, or parking lot, the gas must also filter up through pavement. After filtering up through the ground and pavement, the gas is quickly dispersed by wind. Accordingly, a gas detection device must be extremely sensitive. To detect a natural gas leak under these conditions, a gas detection device should be able to detect trace quantities of gas as low as 1 part per million (ppm).
Second, in addition to wind, a gas detection device must be able to detect gas leaks under varied and extreme environmental conditions. In addition to detecting natural gas in rain, snow, heat, dust, or humidity, the detection device itself must be able to withstand variations in temperature and humidity. Therefore, the device must be rugged and operable under a variety of weather conditions. Although extremely sensitive gas detection devices have proven effective in the confines of the laboratory, these sensitive but fragile devices have not previously been adapted to the field.
Also, although some prior art gas detection devices have been adapted to hostile external environments, these devices have faced static environmental conditions. For example, gas detection devices have been developed to detect emissions from a smokestack or gas levels in a factory. These devices are designed for a specific environment and do not face extreme variations in both temperature and humidity.
Third, unlike laboratory and static environment gas detectors, an effective natural gas detector must be mobile. A natural gas detector must go to the gas, rather than vice versa. More importantly, the gas detection device must be effective when moving very quickly. As previously noted, millions of miles of underground gas pipeline must regularly be surveyed. To cost effectively survey this vast length of pipeline for leaks, a gas detection device must be able to detect trace quantities of gas while being moved very quickly over the pipelines. Because much of the underground natural gas network is located beneath streets, these pipelines are most effectively surveyed by a gas detector mounted on a vehicle.
Currently, natural gas personnel survey over 100,000 miles of gas pipeline by vehicle using a flame ionization unit (FIU). The FIU is mounted on leak survey vehicles. The FIU employs a manifold of sample intake ports, generally located below the front bumper of the vehicle and extending from wheel to wheel. The ports direct samples of air to the FIU sensor. The FIU sensor includes a hydrogen-air flame that creates chemiions from any combustible or oxidizable substance in the intake air including, but not limited to, natural gas. The flame is flanked by two electrodes that collect the ions, resulting in a current. After being suitably amplified, the current is fed to a meter readout and audio alarm.
Although the FIU detector may detect trace quantities of natural gas, the FIU is ineffective at higher vehicle speeds. The leak survey vehicle must travel at a speed from 2-7 miles per hour, depending on the level of sensitivity desired. Typically, for the required sensitivity, the vehicle must travel at approximately 2-3 miles per hour.
Obviously, the productivity of this system is poor. Personnel typically may survey only 5-10 miles per day. In addition, the slow vehicle speed typically disrupts traffic and engenders ill will towards natural gas personnel.
Also, the FIU detector system suffers from a slow response time. The FIU detector system must collect a sample of air, direct the air to the flame, burn any combustibles in the air, and then analyze the ions. Only then is an operator alerted to the presence of a natural gas leak. After the operator is alerted, the vehicle must retrace its path or use alternative detection methods to find the precise location of the offending gas leak. Moreover, because the FIU responds to all combustible substances, the FIU often endures false positive readings.
Accordingly, those skilled in the art of natural gas detection have sought a method and device for detecting natural gas that is highly sensitive, rugged, operable under varied and extreme environmental conditions, mobile, able to be mounted on a vehicle and operated at relatively high vehicle speeds, cost effective, immediately responsive to natural gas leaks, and resistant to false positive readings.